I read through the replies and hopefully I'm not replicating a post. The OP won't be using the HDMI out from the OPPO as it is setup from the factory. The Oppomod adds a card to the PCB which includes it's own seperate I2S output using the HDMI cable. I believe you have to cut an opening in the housing for the new port.
I'm thinking about this mod also myself.
HTH.